Ian Walmsley

Abstract:

We investigate the absorption distribution in a cylindrical gain medium that is pumped by a source of distributed laser diodes by means of a pump cavity developed from the edge-ray principle of nonimaging optics. The performance of this pumping arrangement is studied by using a nonsequential, numerical, three-dimensional ray-tracing scheme. A figure of merit is defined for the pump cavities that takes into account the coupling efficiency and uniformity of the absorption distribution. It is found that the nonimaging pump cavity maintains a high coupling efficiency with extended two-dimensional diode arrays and obtains a fairly uniform absorption distribution. The nonimaging cavity is compared with two other designs: a close-coupled side-pumped cavity and an imaging design in the form of a elliptical cavity. The nonimaging cavity has a better figure of merit per diode than these two designs. It also permits the use of an extended, sparse, two-dimensional diode array, which reduces thermal loading of the source and eliminates all cavity optics other than the main reflector.

Abstract:

The probability density of the single-shot mean Stokes frequency from a linear Raman generator is calculated. It is shown that the fluctuations in the Stokes pulse energy spectrum that arise from the quantum initiation of the Stokes light are reduced in the transient regime of amplification. Also, it appears that saturation of the Raman gain does not reduce the phase fluctuations of the Stokes light below those present in the unsaturated gain (linear) regime.

Abstract:

A continuously pumped Nd:YLF regenerative amplifier has been developed that can amplify 40-psec pulses at a repetition rate of greater than 10 kHz, with an average power in excess of 5 W. Pulse energies are as high as 2.0 mJ at 3 kHz and 640 microJ at 10.5 kHz. The limitation on the amplifier repetition rate that is associated with piezoelectric ringing in LiNbO(3) electro-optics has been overcome by using short-pulsed electric fields (10 nsec) and proper acoustic damping. Regenerative pulse amplification, limited in repetition only by the pump rate of the gain medium, has been achieved. The high repetition rate in regenerative pulse amplification made possible by this development should prove important for signal-processing considerations in a wide variety of pulse-amplification applications.

Abstract:

We have developed a technique to measure the group-delay time of optical components with a temporal resolution of +/-0.1 fsec and a spectral resolution of 0.1 nm over the spectral region 600-640 nm. The group delay is determined from a measurement of the optical path length through the component as a function of wavelength with a phase-locked interferometer.